1. Field of the Invention
This invention relates to a vehicle-board electronic control device that restrains lowering of AD conversion accuracy due to variation and difference of output voltage from a constant-voltage power supply circuit unit provided in a vehicle-borne electronic control device such as engine control device or transmission control device and feeding at least a multi-channel AD converter and a microprocessor, the constant voltage power supply circuit unit being fed by a vehicle-borne battery to generate a predetermined constant-voltage output.
2. Description of the Related Art
In a vehicle-borne electronic control device, improvement in the constant-voltage control accuracy of a constant-voltage power supply circuit unit provided therein is important, for example, for improving the AD conversion accuracy of a multi-channel AD converter and the generation accuracy of various comparison reference voltages.
However, there is a problem that the constant-voltage power supply circuit unit becomes expensive if a constant-voltage output of extremely high accuracy is to be acquired while difference and variation among individual components used are inevitable.
To avoid this problem, the constant-voltage control accuracy is improved by using a constant-voltage power supply unit having constant-voltage control accuracy lower than an expected value and adding an auxiliary unit to prevent at least the lowering of the constant-voltage control accuracy due to the difference and variations among individual components used.
For example, according to Patent Reference 1, “Circuit Device and Method for Setting Adjustment Data of Circuit Device”, in a constant-voltage generator circuit formed as a part of a semiconductor sensor or vehicle engine control unit (ECU), a reference voltage VBGR, which is an output voltage of a reference voltage generator circuit formed by a band gap regulator, is amplified by an operational amplifier to acquire a predetermined constant-voltage output Vcc. Also, adjustment data is written into an EPROM memory to correct the individual difference and variations of the reference voltage VBGR, and the amplification factor of the operational amplifier is increased or decreased by this adjustment data to acquire the predetermined constant-voltage output Vcc.
The device and method according to Patent Reference 1 not only improve the constant-voltage control accuracy but also provide an additional function of adjusting the threshold value of a reset circuit, interlocked with the adjustment data.
Since the constant-voltage output also varies depending on the ambient temperature of the constant-voltage power supply circuit unit, temperature compensation control to restrain this variation is necessarily carried out. However, perfect temperature compensation control is difficult. If temperature compensation of extremely high accuracy is to be performed, the constant-voltage power supply circuit unit becomes expensive. For example, Patent Reference 2, “Stabilized Power Supply Circuit”, discloses a technique of generating plural constant-voltage circuits with their output voltages temperature-compensated by using a constant-current circuit having a positive temperature coefficient and a characteristic compensation element having a negative temperature coefficient where a band gap voltage is used. However, 100% temperature compensation cannot necessarily be performed by such band gap circuit.
Patent Reference 1: JP-A-2002-366238 (Paragraph 0009, FIG. 5)
Patent Reference 2: JP-A-8-16265 (FIG. 1, Abstract)
In Patent Reference 1, “Circuit Device and Method for Setting Adjustment Data of Circuit Device”, the variation of the output voltage due to the difference and variation among individual components used is corrected by initial adjustment. However, there is a problem that the output voltage varies on the basis of the difference between the ambient temperature at the time of correction and the temperature during the use of the device.
In Patent Reference 2, “Stabilized Power Supply Circuit”, the variation of the output voltage is restrained by the temperature compensation control. However, it does not provide sufficient temperature compensation. For example, because of the difference and variation among individual temperature compensation control components, the temperature compensation characteristic changes even in the same control circuit, and individual products output different output voltages.